The process of lost wax casting has been used for hundreds of years with very little change. In recent years, however, new developments have caused considerable progress, to the delight of the modern goldsmith. Research and development in this field will certainly continue, as all producers aim for products of increasingly higher quality and lower manufacturing costs.
The dream of all goldsmiths is to obtain castings which are completely and consistently perfect. Although there is no process today which can guarantee such a result, it is possible to reach close to 98 to 99 percent accuracy by using the necessary equipment and techniques in the appropriate, way,-following manufacturers’ instructions, using the required products in the proper amounts, controlling times and temperatures, etc…Most casting errors, like car accidents, are due to the human factor, not the equipment used.
Recent technical developments have brought significant improvements to the lost wax process by using new materials, instruments and processes.
· Flexible modeling wax, which can also be injected in rubber molds to create multiple pieces or basic models which can be subsequently altered to create many slightly different items.
ADVANTAGES: Easy to work with; reduced labor costs.
DISADVANTAGES: Not yet commercially available.
· Modeling resin to create additional parts or details for a basic model, when it is necessary to achieve seamless junctions.
ADVANTAGES: Perfectly conjoining pieces; can be worked with like a hard wax; can be melted.
DISADVANTAGES: Commercially available only through suppliers of dentistry products; very expensive. (Figure 1)
· Computerized systems which make models using various techniques, at different levels of complexity and span a range of prices.
· Silicone rubber for mold making, available with different levels of hardness, shrieking, resistance to tearing and to heat, both colored and transparent.
ADVANTAGES: More accurate copies of the original model; does not require spray or talcum powder; faster and easier to make; more durable.
DISANVANTAGES: More difficult to burn if modifications are necessary. (Figure2)
· Highly fluid and flexible injection wax, which allows perfect casting of thin objects and filigree work.
ADVATAGES: Can be injected at very low pressure levels; ideal for light-weight jewelry.
DISADVANTAGES: More expensive than conventional wax. (Figure 3)
· Increasingly fine investment, which are easier to mix and contain de-oxidizing substances, to obtain de-oxidized castings with extremely smooth finish even when using simple alloys.
ADVANTAGES: Less finishing work required.
DISADVANTAGES: Commercially available only through suppliers of dentistry products; very expensive. (Figure 4)
· Product to be mixed-in with regular investment, suitable for vacuum casting, which increases the micro-porosity of the plaster and de-oxidizes metals.
ADVANTAGES: Casting can take place at lower temperatures, for both cylinder and metal, without defects; less porosity; ideal for casting thin objects and filigree and extremely smooth, therefore requires less finishing work.
DUSADVANTAGES: It is extremely important to follow the mixing instructions very carefully.
· Liquid to be added to the investment mix for casting with stones.
ADVANTAGES: Protection for stones, especially diamonds; allows to increase temperatures by 150°C, therefore avoiding porosity due to unburned residues.
DISADVANTAGES: It is extremely important to follow the mixing instructions very carefully. (Figure 5)
· Pre-alloys, or additives for alloys, to eliminate or reduce porosity and obtain entirely de-oxidized castings, especially suitable for castings with stones.
ADVANTAGES: Better quality casting, which does not need to be treated with acid to remove the investment; may be melted again adding very little (30 percent) new alloy; does not harden if cooled slowly; easier and faster finishing process.
DISADVANTAGES: It is extremely important to follow the mixing instructions very carefully; additional cost. (Figure 6)
· Entirely automated, computer controlled, melting and casting equipment which perform the process in oxygen-free environment and utilize suction and high pressure at the casting stage.
ADVANTAGES: Greater control of each step; reduced porosity; improved and more consistent product quality; easy to operate; less opportunity for human errors; ideally suited for large scale productions.
DISADVANTAGES: Initial programming and testing of the equipment is tome consuming; high cost.
· Optical pyrometer for reading temperatures from a distance (50 to 100 cm). This is a control instrument which should be used in every department casting gold and platinum.
ADVANTAGES: Extremely fast and accurate measurement of temperatures between 500° and 2,200°C from a distance; very easy to use.
DISADVANTAGES: High cost.
These are only a few of significant innovations in the lost wax casting field. Many more are currently being developed and these will be described as soon as they will be readily available.
All of the above notwithstanding, whatever the product, instrument or technique
chosen, the best results will be achieved only by scrupulously following the instruction manual and the manufacturer’s recommendations.
The next article will feature another innovative instrument and technique-the laser. We will look at how it can help achieve high quality products, what it is best suited for, and how to use it efficiently. (Figure 7)